Characterizing complex large deformation of flexible skin wings during shear variable-sweep under load using improved stereo-DIC

Monitoring the shape and deformation of morphing wings is vital for ensuring multi-mission flight and safety operation. During the morphing process, the complex deformation of the flexible skin wing usually involves large amounts of movement, shearing, bending, and distortion. This paper proposes an improved stereo-digital image correlation measurement system designed to characterize full-field complex large deformation of flexible skin shear variable-sweep wings (SVSWs). By minimizing reference image updating frequency using the proposed conditional incremental strategy, effectively addressing the computational failures caused by image decorrelation due to complex large deformations. To improve tracking efficiency and accuracy of uncoded targets in complex backgrounds, an automatic subpixel detection method for circular diagonal targets is presented. A series of experiments are performed on a 1200 mm span flexible skin SVSW to verify the proposed methods. The results show that the length and angle measurement accuracies are better than 0.11 mm and 0.05°, respectively. Based on the measured morphing geometry parameters, displacement and strain fields, the structural integrity and morphing performance of the wing under different loads are discussed. During the shear variable-sweep process, the wingtip load dominates the deflection distribution, while its effect on the strain distribution is relatively minor. The proposed method and system can provide reliable data support for the structural optimization design and safety evaluation of such morphing wings.